Gardeners inspired by TV makeover shows to import tropical plants have unleashed a deadly disease threatening to wipe out trees across Sussex, scientists believe.

Fans of programmes such as BBC1's Ground Force, starring Charlie Dimmock, are bringing together plants which never normally come into contact, causing the mutation of the fungus leading to sudden oak death.

The microscopic pathogen Phytophthora ramorum has already wiped out thousands of oak trees in the United States, sparking fears the English oak may suffer the same fate. British trees were thought to be immune to the disease until it was discovered in a southern red oak in woods near Crawley last year.

There have been 30 cases of sudden oak death in Sussex - the highest number in any area of Britain - according to officials at the Department for Environment, Food and Rural Affairs and the Forestry Commission.

Experts have traced the source of the threat to popular garden plants such as rhododendrons and viburnums which are imported in bulk from Asia.

In this week's edition of New Scientist, Clive Brasier, a scientist at the commission, says virulent forms of pathogenic fungi can emerge when different strains from around the world are brought together in nurseries.

He said: "The disease is now becoming serious and widespread across Europe."

In their natural habitats, Phytophthoras are harmless to trees. They can turn nasty, however, if introduced to species they have never encountered before.

The New Scientist said: "Today, almost everyone's small plot is filled with exotics, a trend fuelled by TV makeover shows and gardening magazines.

"This obsession with the exotic has created a multi-billion dollar global industry and the risk of importing lethal pathogens is far higher."

Phytophthora ramorum can spread by rain splashing from one plant to the next and in soil carried on vehicles, machinery or animals.

Infected trees appear to bleed to death as sap spills from them. They can die within months.